I usually use 2 cans. I pour 1 can in the crankcase 1 day before I plan on changing my oil. Then 1/2 can in the fuel system. then the other 1/2 can sucked in through the brake booster let her sit for 30-45 min. Start her up and let the fun begin. Then change the oil.
There's a certain amount you're supposed to put into the crankcase, I don't think you're supposed to use a whole can. This was really helpful.
Grand Prixs Of North America • View topic - Seafoam writeup